The present invention relates to DC/DC power supply controllers, and more particularly to regulated capacitive-only or capacitive/inductive power converters for integrated power management systems.
Advances in electronics technology have enabled the design and cost-effective fabrication of portable electronic devices. Thus, usage of portable electronic devices continues to increase as do the number and types of products. Examples of the broad spectrum of portable electronic devices include pagers, cellular telephones, music players, calculators, laptop computers, and personal digital assistants, as well as others.
The electronics in a portable electronic device generally require direct current (DC) electrical power. Typically, one or more batteries are used as an energy source to provide this DC electrical power. Ideally, the energy source, such as consumer batteries of standard sizes such as AAA, AA, A, C, D and prismatic 9V, would be perfectly matched to the energy requirements of the portable electronic device. Improvements in electrochemical formulations, such as alkaline and lithium electrochemical cells, have satisfied to a limited degree needs for batteries having increased shelf life, increased stored charge, and peak capacity. With even these changes, a number of deficiencies exist.
For instance, many portable devices include integrated circuits having a minimum voltage level in order to operate. Voltaic cells such as electrochemical cells have an output voltage level that generally declines over the service life of the battery. Generally, a significant portion of the battery service life occurs after the output voltage of the battery has declined below the minimum voltage level of the device. In some instances, the wasted service life is as much as 80%.
In addition, most often the voltage and current from the batteries are unsuitable for directly powering the electronics of the portable electronic device. For example, the voltage level determined from the batteries may differ from the voltage level required by the device electronically. In addition, some portions of the electronics may operate at a different voltage level than other portions, thereby requiring different energy source voltage levels. Still further, batteries are often unable to respond quickly to rapid fluctuations in current demand by a device.
A typical arrangement is shown in FIG. 1 for a portable electronic device 10 that includes an energy source 12, such as one or more batteries, and a load device 14, such as the internal electronics that require electrical power. Interposed between the energy source 12 and the load device 14 is a power supply 16 that may perform a number of functions. For example, a power converter 20, depicted as integral to the power supply 16, provides the necessary changes to the power from the energy source 12 to make it suitable for the load device 14.
With respect to the types of power conversion required, the power converter 20 may xe2x80x9cstep upxe2x80x9d (i.e., boost) or xe2x80x9cstep downxe2x80x9d the voltage. That is, the converter 20 may increase or decrease an input voltage VS from the energy source 12 across a pair of input terminals 24, 25 to an output voltage VO provided to the load device 14 across a pair of output terminals 26, 27. The power converter 20 may also store an amount of energy to satisfy a brief spike or increase in demand by the load device 14 that the energy source 12 is unable to provide.
The power converter 20 may also regulate the output voltage VO, keeping it close to the desired output voltage level and reducing rapid fluctuations that may cause detrimental noise or cause undesirable performance of the load device 14. Such fluctuations may occur due to changes in demand by the load, induced noise from external electromagnetic sources, characteristics of the energy source 12, and/or noise from other components in the power supply 16.
Conventionally, switching power converters 20 are used in portable devices due to their suitable size and cost. However, capacitive-only charge pump or inductive/capacitive switching power converters 20 typically rely upon oscillatory switching between a charge and discharge state to transfer power from an energy source such as an electrochemical voltaic cell 12 to a load device 14. Each switching of state incurs a significant consumption of power that reduces the shelf-life of the voltaic cell.
In addition, although generally suitable for being portable, such power converters 20 still adversely impact the size, weight and cost of the portable device.
Moreover, the power converters typically cannot be optimized for a wide array of available types of electrochemical voltaic cells 12 (e.g., lithium, alkaline). Consequently, such power converters 20 generally only regulated voltage at a consider loss of efficiency or boost the voltage derived from the cell 12 in an unregulated fashion.
Consequently, a significant need exists for a power converter that more efficiently provides an efficient, regulated output voltage for portable electronic devices.
The invention overcomes the above-noted and other deficiencies of the prior art by providing an apparatus and method for a dynamically controlled inductive DC/DC power converter that efficiently transfers power from an energy source as demanded by a load device.
The present invention meets these and other needs by providing a battery with a built-in, dynamically-switched capacitive device. More particularly, a power converter is provided to adjust an output voltage (VO) across a positive and negative terminal of the battery dynamically based on the electrical load using an efficient switching approach, with both the power converter and switching approach optimized for incorporation within a battery container. Furthermore, the power converter would be adaptable to a number of battery types.
In some of our previous inventions, introduction of electronic circuitry within the container of a battery, especially standard-sized consumer batteries, was shown to provide a number of advantages such as by regulating the output voltage. Specifically, the following co-pending and commonly owned applications were all filed on Apr. 2, 1998: U.S. Ser. No. 09/054,192, entitled PRIMARY BATTERY HAVING A BUILT-IN CONTROLLER TO EXTEND BATTERY RUN TIME, naming Vladimir Gartstein and Dragan D. Nebrigic; U.S. Ser. No. 09/054,191, entitled BATTERY HAVING A BUILT-IN CONTROLLER TO EXTEND BATTERY SERVICE RUN TIME naming Vladimir Gartstein and Dragan D. Nebrigic; U.S. Ser. No. 09/054,087, ENTITLED BATTERY HAVING A BUILT-IN CONTROLLER, naming Vladimir Gartstein and Dragan D. Nebrigic; and U.S. Provisional Application Serial No. 60/080,427, entitled BATTERY HAVING A BUILT-IN CONTROLLER TO EXTEND BATTERY SERVICE RUN TIME, naming Dragan D. Nebrigic and Vladimir Gartstein. All of the aforementioned applications are hereby incorporated by reference in their entirety.
In another of our inventions, we showed the advantage of incorporating electronic circuitry for additional advantages such as providing enhanced indications of the state of charge of the battery. Specifically, the co-pending and commonly owned application filed on Apr. 23, 1999: U.S. Ser. No. 09/298,804, entitled BATTERY HAVING A BUILT-IN INDICATOR, naming Dragan D. Nebrigic and Vladimir Gartstein, wherein the aforementioned application is hereby incorporated by reference in its entirety. Also discussed was an inductive-capacitive power converter that advantageously increased the battery output voltage.
We have since discovered that a capacitance-only power converter based upon a charge pump had a number of desirable attributes for applications requiring the increase in battery output voltage, especially for the versions described below which provide for size and power requirements of a battery.
Furthermore, in an illustrative version, the power converter utilizes a load capacitor that receives a transfer of charge from a fly capacitor. More particularly, the fly capacitor is switched dynamically to accommodate varying loads on the load capacitor to efficiently transfer charge. Specifically, the power converter comprises a charge pump including a switching matrix controlling a fly capacitor wherein the fly capacitor is switched to charge mode electrically parallel to a voltaic cell of the battery. Thereafter, the switching matrix switches to a discharge mode where the potential of the fly capacitor is additively placed in series with the voltaic cell, and the combination is electrically coupled across the load capacitor to discharge the stored charge in the fly capacitor into the load capacitor.
As a further aspect, in order to increase the current output capacity of the load capacitor, the switching of the fly capacitor is dynamically performed by a switching matrix controller, rather than merely oscillating the state of the switching matrix without regard to electrical load. Dynamic control allows for power conservation during periods of low power demand on the battery.
Another aspect is to dynamically control the switching matrix by incorporating a comparator into the switching matrix controller. In some versions, also provided is a voltage reference and temperature compensation for the voltage reference for the comparator to use in comparing the output voltage to a predetermined threshold.
In an additional aspect, an internal power supply is provided to bias the power converter, especially for voltaic cells having a relatively low nominal voltage.
In order to achieve low power consumption and to operate within the small volume typical of some batteries, the power converter is largely fabricated as an Application Specific Integrated Circuit (ASIC). Moreover, Field Effect Transistors (FET) are described that have the capacity for the peak battery current yet provide a low power consumption.
More particularly, we have found that dynamically controlling a power converter as required by the load on a battery provides additional peak capacity and/or increased power efficiency, among other advantages. In addition, such a dynamic switching lends itself to a wide range of voltaic cells (e.g., electrochemical cells such as lithium, zinc acid, alkaline, etc.; electro mechanical cells, solar cells; etc.).
Consistent with yet a further aspect of the invention, dynamic control of a inductive-capacitive DC/DC power converter includes sensing an adequate state of charge of a load capacitor across the output terminals and stopping pulse width modulation control of the switching of an inductive element, a synchronous rectifier and a switch to reduce power consumption by the power converter.
These and other advantages of the present invention will become apparent in the discussion below.